I don't know how many people do this, but for me, on commercial radio shows that I listen to a lot, I get a feel for the length of spot breaks. When the commercials start, I go elsewhere for what I think is about the time to return. I'm, usually, pretty close. If I come back too early, I still know that there can't be that many commercials, and other non-show content left. If I misjudge and come back a little late, I'll either be into an early part of the first song after the break, or I'll know what is being talked about, and can easily catch up.